A novel infrared thermography-based method for measuring suction at evaporating soil surfaces

Soil surface suction evolves during evaporation until heat and humidity equilibrium is established between the atmosphere and the soil. Accordingly, the suction is a key indicator of the thermo-hydro-mechanical (THM) behaviour of soils under atmospheric influences. However, this variable and its two-dimensional distribution are difficult to measure using traditional destructive methods and non-destructive techniques that impose strict constraints on sample size. A novel method is proposed to estimate soil surface suction under evaporation using infrared thermography. In this approach, an infrared camera captured soil surface temperature variations in real time, which were integrated into a typical THM theoretical framework involving the energy balance and boundary flux equations to calculate the suction analytically. Despite the assumption of several fixed model parameters to simplify the procedure, the calculated suction values agree well with physical measurements, particularly under conditions where soil intrinsic properties govern evaporation. The method was further validated by increasing the soil’s lateral size, which introduced spatial variability in the THM behaviour. The resulting non-uniform suction field indicates that lateral pore water transport contributes to the stabilisation of local evaporation, thus producing a stable yet spatially non-uniform thermal field across the soil surface. Given these validations, the proposed method holds significant potential for investigating regional atmosphere-soil interactions and improving early warning systems for geotechnical hazards, as it enables portable, instantaneous and non-contact suction measurements without lateral size constraints.